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Balancing processing needs, power and integration in next-gen handsets

Posted: 18 Dec 2006 ?? ?Print Version ?Bookmark and Share

Keywords:wireless technology? handset design? handsets? designing cellphones? digital signal processing?

By Roman Polz
Agere Systems

The one constant in cellphone design is change. One of the latest examples of this was the introduction recently of an assortment of creative new cellphones now being designed and envisioned to be in vogue around the world. These include a cellphone that enables compact disk-quality music at entry-level cellphone prices; another that has a necklace shape with beads lighting up to signal an incoming call; and another that looks like macaroons and cakes.

These new types of cellphone designs are changing the way cellphone designers tackle some of the most difficult challenges. These challenges include:

? How to provide faster digital and analog processing speeds;
? How to deal with all sorts of convergence of services technologies and applications;
? How to keep power consumption low; and
? Whether to integrate DSP and radio frequency technology on the same design.

This article will discuss these latest design trends and their implications in more detail.

Dedicated versus shared processing
A hot issue in designing creative new types of cellphones centers on how to partition chip functions to maximize horsepowerwithout increasing power consumption. One architectural approach involves an entry-level cellphone that comes with CD-quality music. This design integrates on a single chip the DSP and microcontroller functions. The microcontroller functions have separate duties. One, integrated with the DSP, is an engine that handles communications processing such as the actual cellphone voice signals. The other microcontroller's sole responsibility is handling applications processing such as music, multimedia and Internet access.

Using a dedicated applications processor separate from the communications engine reduces cellphone manufacturer's product development costs and boosts overall processing speed. This segmentation allows each processor to be fully dedicated to its particular function and eliminates complications, such as increased integration and debug times that often occur with designs that offer combined communications and applications processors. The segmentation also eliminates the interdependencies that result when domains share processing and memory space. In addition, the boosted horsepower provided by the dedicated applications processor enables several key benefits including:

  • Making possible phone calls and data downloads while playing music or video games.

  • Easing of applications software code development, test and verification for cellphone manufacturers because it doesn't impact the core communications engine.

  • Reducing power consumption because the more power hungry applications processor can be powered down the majority of the time a phone is on.

  • Liberating cellphone manufacturers to focus on developing applications and man-machine interfaces without worrying about impacting the communications engine.

Cellphone convergence
Widespread debate has heated up in the recent months about what device will ultimately be the center of the most cellphone convergence. These devices being considered include cellphones, personal digital assistants, Blackberries, wireless LANs, and music players. One question is whether the music player handheld device become a cellphone or will the cellphone become a music handheld device? The truth is both will probably happen.

Example of a CD-quality EDGE cellphone chip separating the communications processing from the applications processing for maximizing efficiency

From an engineering perspective, however, there should be no doubt that much architectural planning going forward will be centered on the cellphone. "The cellphone continues to be the physical and market magnet pulling in the functionality of digital cameras, MP3 players, GPS navigators, Bluetooth, FM radio, digital TV and even cordless phones, and is quickly becoming the dominant market for each and all of these functions," said Carter L. Horney, principal author of a new Forward Concepts cellphone study called "Cellular Handset and Chip Markets '06." With all this cellphone applications convergence continuing at a frantic pace, the cellphone designer will have to be nimble and smart in deciding what to integrate and what to leave as separate chips. They will have to keep their sights set on building higher performance, lower cost, and lower-power-consuming devices.

Cellphones are stealing communications and entertainment functions from personal computers. So the cellphone designer would benefit by being familiar the latest PC design trends and applications. Designers will have to figure out how to integrate GPS navigators onto cellphones, because that market is gathering momentum. But gaining particularly fast momentum is the design of CD-quality music capability into cellphones, tracking with the amazingly popular small and easy-to-use music devices among consumers. Cellphones can already store hundreds of songs.

To enable this, high-quality digital acoustics hardware and software will have to be developed to make the quality of the music CD quality so these cellphones will be appealing to consumers. In addition to requiring CD-quality music, finding the right song, the exact one the user wants quickly and easily, among the hundreds stored on the cellphone will be an important, differentiating feature.

Power consumption
The amount of power a cellphone consumes lies at the heart of the architectural design trade-off issue. This trend will continue as new, more creative designs come to market. Cellphones need to have extended battery life and not burn up the phone. Simultaneously, they need faster possessing speed to handle higher-bandwidth multimedia services such as mobile TV and music.

The way to attack this problem, which applies also to new creative cellphone designs, is no longer focused on the silicon chip at the circuit level. What's crucial now is to address this problem from a system-level architectural platform point of view, because all of the various hardware and software aspects of the cellphone have to be factored into the design analysis to get more accurate, ideal solutions. This system-level approach opens more possibilities for innovations in design to keep power low and bandwidth high.

The power consumption design issues relate to a trend now emerging in which reducing the number of features on a cellphone is being considered wise. The notion is that cellphones should only be designed with features and functions that are most widely used and eliminate other functions, which are numerous. By doing so, the cellphone consumes less power. The most recent cellphones are no longer designed to pack every function into the same device. A growing number are being custom designed and segmented to play high-quality music, do high-speed Internet browsing, or take digital camera photos, but not necessarily do all three on one cellphone.

"Find just one feature or a tightly combined set of features that appeal to users," said a recent report by International Data Corporation. "As vendors introduce mobile phones packed with an array of features such as embedded cameras, MP3 players, streaming video playback, and many others, the resulting products have been a "Swiss army knife" of multiple uses. "Most users, however, find that they will use just one feature or one set of features that appeal to them. What results is under-usage of the device and operators that are not experiencing the full average revenue per user potential the device presents. At the same time, phones with just one particular feature have been resonant with users who are more likely to use that feature more often."

Consider the necklace. To design a cellphone shaped like a necklace, cellphone designers will have to figure out innovative ways to shrink the components to smaller sizes and shapes while powering them enough so the necklace doesn't wear out its battery charge for several days or weeks. The necklace also can't use too much power or it could irritate the person wearing it.

Integrate baseband with RF?
For at least the past 10 years the semiconductor industry has been conceptualizing and working to deliver a cellphone architectural nirvana: combining radio frequency and DSP silicon into one SoC. This integration has already begun to happen in the ultra-low-cost cellphone segment. This is because of the SoC benefits of fewer components, lower costs, and lower power consumption. Achieving this system on a chip is probably too much to ask in the next few years given the design complexity of new, creative cellphones. No single-chip solution is likely to materialize on the market before 2008.

Other factors will push out this integration. One is that some companies specialize in designing basebands, others RF, and some don't make both types of chips. This lack of industry-wide knowledge of both technologies will continue to slow integration progress. Company relationships also factor in. A company that has cellphone basebands but not RF may consider buying silicon from RF chip providers. But so far that doesn't look to be financially feasible because RF prices are generally too high. If those prices came down, the baseband provider would be more likely to collaborate with the RF provider, and the progress toward bringing to fruition the single-chip wonder would accelerate.

About the author
Roman Polz
is a senior manager for the mobility division of Agere Systems. Comments may be sent to polz@agere.com.




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